Reputable Carbon Offset Organizations

Look at your airline's strategy on carbon credits. I seem to recall having this posed as a question on flights, so the website must have something established for contributions.

Alternatively, a quick google search provided this
https://www.dummies.com/home-garden/green-living/how-to-fly-carbon-neutral-an-eco-friendly-travel-option/
The cynic in me questions whether the 'programs' really see the donations or whether the money gets caught up in administration costs (like 3rd party volunteer and donation organizations), so this article gives some insight of what to look for.
I will say, having spent time in Tanzania and know Maasai may have to walk 7 kilometres at times to get wood for their fires, and of course, the deforestation because of needing wood for their fires and their need for cattle grasslands, I am partial to the efficient cook stove projects. You can imagine some charcoal fire in a small enclosed hut and what it does to lungs and eyes. These new efficient stoves can make a positive impact.

Checking with the airline web site was a fantastic idea. I'm flying Delta and United. The United carbon calculator seemed to work well enough, though I had to put each leg of my trip in individually.

Delta is donating to The Nature Conservancy, if one uses their program. I wasn't impressed with their rating on Charity Navigator.
United is donating to Conservation International, which has good marks on Charity Navigator.

When I read about carbon offset schemes(usually involving planting trees) I can't stop thinking of this scene from one of my favourite movies, unfortunately I can't find this hilarious scene.

www.jewishhumorcentral.com/2016/01/funniest-jewish-film-moments-tu-bshvat.html

https://www.nytimes.com/2000/07/03/world/arboreal-scandal-in-israel-not-all-of-the-trees-planted-there-stay-planted.html

I think there is no way around reducing your carbon footprint. Fly less, drive electric car, hike, bike, sail, kayak, hitchhike/ride share, take trains.

I had intended to add that what you can control the most is your day to day impact (as mentioned above). If you are lucky enough - use public transit. Stop buy new 'stuff' or clothes. Reusing uses a lot less energy than buying new.
All that being said, a few years ago I did something called the 'one ton challenge' https://en.wikipedia.org/wiki/One-Tonne_Challenge.
I failed miserably, despite using public transit, having added a number of energy saving home devices, reusing stuff, recycling...but the reason I failed was because I live alone - in a real house. Despite it being small, just the ambient energy made it a failure.

So, do what you can and what makes you feel better. You may want to try to find a similar challenge or test to take to see where you can make the biggest savings for your buck in the long term, rather than just when you fly.

I think there is no way around reducing your carbon footprint

Sure there is. Live in an area of the country with excellent public transportation so you don't have to drive everywhere you want to go let alone even owning a car. If one really wants to effect concrete change regarding improving the environment, actually DO something to effect that change. Improvement starts with each of us.